Device and method for noninvasively determining the hematocrit value of a subject

Abstract

The present invention relates to a device and method for noninvasively determining the hematocrit value of a subject. The device comprises a light source ( 22, 23 ) for emitting light onto a skin area of the subject, said light comprising first light at a first wavelength in a first wavelength range between 500 and 1000 nm and second light at a second wavelength in a second wavelength range between 1000 and 2000 nm, a reflection detector ( 24 ) for detecting light reflected from said skin area of the subject in response to light illumination by said light source, a transmission detector ( 25 ) for detecting light transmitted through said skin area of the subject in response to light illumination by said light source, a processing unit ( 31 ) for deriving plethysmography, PPG, signals for said first and second wavelengths from the light detected by said reflection detector ( 24 ) and said transmission detector ( 25 ), and an analysis unit ( 32 ) for determining the hematocrit value of the subject from said PPG signals.

The invention claimed is: 
     
       1. A processor for noninvasively determining the hematocrit value of a subject, the processor comprising:
 a processing unit configured to derive plethysmography, PPG, signals for a first wavelength and a second wavelength from detector signals acquired by detection of light reflected from a skin area of the subject in response to light illumination and light transmitted through said skin area of the subject in response to said light illumination,
 wherein said light illumination includes a first light at a first wavelength in a first wavelength range between 500 and 1000 nm and a second light at a second wavelength in a second wavelength range between 1000 and 2000 nm, and 
 wherein said processing unit is further configured to derive a first PPG signal from a first detector signal acquired by detection of the reflected light at the first wavelength, a second PPG signal from a second detector signal acquired by detection of the reflected light at the second wavelength, a third PPG signal from a third detector signal acquired by detection of the transmitted light at the first wavelength, and a fourth PPG signal from a fourth detector signal acquired by detection of the transmitted light at the second wavelength; and 
 
 an analysis unit configured to determine the hematocrit value of the subject from said PPG signals, wherein said analysis unit is further configured to:
 i) determine relative pulsatile absorptions for said first to fourth PPG signals by forming a first to fourth pulsatile absorption ratio of the AC component to the DC component of the respective PPG signals, to obtain a first ratio by adding the first and third pulsatile absorption ratios obtained from the PPG signals obtained from the light at the first wavelength, to obtain a second ratio by adding the second and fourth pulsatile absorption ratios obtained from the PPG signals obtained from the light at the second wavelength, and to obtain a final ratio by dividing the first ratio by the second ratio and to determine the hematocrit value of the subject from said final ratio; or 
 ii) determine relative pulsatile absorptions from said first to fourth PPG signals by forming a third ratio of the sum of the AC components of the first and third PPG signals and the sum of the DC components of the first and third PPG signals and by forming a fourth ratio of the sum of the AC components of the second and fourth PPG signals and the sum of the DC components of the second and fourth PPG signals, and to obtain a final ratio by dividing the third ratio by the fourth ratio and to determine the hematocrit value of the subject from said final ratio. 
 
 
     
     
       2. The processor of  claim 1 , wherein said analysis unit is configured to use said final ratio to determine the corresponding hematocrit value from at least one of a look-up table or a calibration curve. 
     
     
       3. A device for noninvasively determining the hematocrit value of a subject, the device comprising:
 a light source for emitting light onto a skin area of the subject, said light including a first light at a first wavelength in a first wavelength range between 500 and 1000 nm and a second light at a second wavelength in a second wavelength range between 1000 and 2000 nm; 
 a reflection detector for acquiring detector signals by detecting light reflected from said skin area of the subject in response to light illumination by said light source; 
 a transmission detector for acquiring detector signals by detecting light transmitted through said skin area of the subject in response to light illumination by said light source; and 
 the processor of  claim 1  configured for processing the detector signals acquired by said reflection detector and said transmission detector for noninvasively determining the hematocrit value of the subject. 
 
     
     
       4. The device of  claim 3 , wherein said reflection detector and said transmission detector are configured to simultaneously detect light and wherein said processing unit is further configured to derive PPG signals from detector signals generated from simultaneously detected light. 
     
     
       5. The device of  claim 3 , wherein said light source includes a first light unit for emitting first light onto the skin area of the subject at said first wavelength and a second light unit for emitting second light onto the skin area of the subject second light at said second wavelength. 
     
     
       6. The device of  claim 5 , wherein the two light units are configured to illuminate the skin area alternatingly. 
     
     
       7. A processing method for noninvasively determining the hematocrit value of a subject, the processing method comprising:
 deriving plethysmography, PPG, signals for a first wavelength and a second wavelength from detector signals acquired by detection of light reflected from a skin area of the subject in response to light illumination and light transmitted through said skin area of the subject in response to said light illumination,
 wherein said light illumination includes a first light at a first wavelength in a first wavelength range between 500 and 1000 nm and a second light at a second wavelength in a second wavelength range between 1000 and 2000 nm, and 
 wherein a first PPG signal is derived from a first detector signal acquired by detection of the reflected light at the first wavelength, a second PPG signal is derived from a first detector signal acquired by detection of the reflected light at the second wavelength, a third PPG signal is derived from a first detector signal acquired by detection of the transmitted light at the first wavelength, and a fourth PPG signal is derived from a first detector signal acquired by detection of the transmitted light at the second wavelength; and 
 
 determining the hematocrit value of the subject from said PPG signals, wherein said step of determining the hematocrit value of the subject from said PPG signals includes:
 i) determining relative pulsatile absorptions for said first to fourth PPG signals by forming a first to fourth pulsatile absorption ratio of the AC component to the DC component of the respective PPG signals, obtaining a first ratio by adding the first and third pulsatile absorption ratios obtained from the PPG signals obtained from the light at the first wavelength, obtaining a second ratio by adding the second and fourth pulsatile absorption ratios obtained from the PPG signals obtained from the light at the second wavelength, and obtaining a final ratio by dividing the first ratio by the second ratio and to determine the hematocrit value of the subject from said final ratio; or 
 ii) determining relative pulsatile absorptions from said first to fourth PPG signals by forming a third ratio of the sum of the AC components of the first and third PPG signals and the sum of the DC components of the first and third PPG signals and by forming a fourth ratio of the sum of the AC components of the second and fourth PPG signals and the sum of the DC components of the second and fourth PPG signals, and obtaining a final ratio by dividing the third ratio by the fourth ratio and to determine the hematocrit value of the subject from said final ratio. 
 
 
     
     
       8. A method for noninvasively determining the hematocrit value of a subject, the method comprising:
 emitting light onto a skin area of the subject, said light including a first light at a first wavelength in a first wavelength range between 500 and 1000 nm and a second light at a second wavelength in a second wavelength range between 1000 and 2000 nm; 
 acquiring detector signals by detecting light reflected from said skin area of the subject in response to light illumination by said light source; 
 acquiring detector signals by detecting light transmitted through said skin area of the subject in response to light illumination by said light source; and 
 in accordance with the processing method of  claim 7 , processing the detector signals acquired by detecting the reflected light and the transmitted light for noninvasively determining the hematocrit value of the subject. 
 
     
     
       9. A non-transitory machine-readable storage medium encoded with instructions for execution by at least one processor, the non-transitory machine-readable storage medium comprising instructions to carry out the steps of the method of  claim 7 . 
     
     
       10. A system for noninvasively determining the hematocrit value of a subject, the system comprising:
 a processor configured to derive plethysmography, PPG, signals for a first wavelength and a second wavelength from detector signals acquired by detection of light reflected from a skin area of the subject in response to light illumination and light transmitted through said skin area of the subject in response to said light illumination,
 wherein said light illumination includes a first light at a first wavelength in a first wavelength range between 500 and 1000 nm and a second light at a second wavelength in a second wavelength range between 1000 and 2000 nm, and 
 wherein said processor is further configured to derive a first PPG signal from a first detector signal acquired by detection of the reflected light at the first wavelength, a second PPG signal from a second detector signal acquired by detection of the reflected light at the second wavelength, a third PPG signal from a third detector signal acquired by detection of the transmitted light at the first wavelength, and a fourth PPG signal from a fourth detector signal acquired by detection of the transmitted light at the second wavelength; and 
 an analyzer configured to determine the hematocrit value of the subject from said PPG signals, wherein said analyzer is further configured to: 
 i) determine relative pulsatile absorptions for said first to fourth PPG signals by forming a first to fourth pulsatile absorption ratio of the AC component to the DC component of the respective PPG signals, obtain a first ratio by adding the first and third pulsatile absorption ratios obtained from the PPG signals obtained from the light at the first wavelength, obtain a second ratio by adding the second and fourth pulsatile absorption ratios obtained from the PPG signals obtained from the light at the second wavelength, and obtain a final ratio by dividing the first ratio by the second ratio and to determine the hematocrit value of the subject from said final ratio; or 
 ii) determine relative pulsatile absorptions from said first to fourth PPG signals by forming a third ratio of the sum of the AC components of the first and third PPG signals and the sum of the DC components of the first and third PPG signals and by forming a fourth ratio of the sum of the AC components of the second and fourth PPG signals and the sum of the DC components of the second and fourth PPG signals, and obtain a final ratio by dividing the third ratio by the fourth ratio and to determine the hematocrit value of the subject from said final ratio. 
 
 
     
     
       11. The system of  claim 10  wherein said anaylzer is further configured to use said final ratio to determine the corresponding hematocrit value from at least one of a look-up table or a calibration curve.